Multiplexer, image projection apparatus using the multiplexer and image projection system

ABSTRACT

To provide a multiplexer that makes it possible to achieve a reduction in size and that minimizes the influence of the expansion of laser light on a multiplexing unit. A multiplexer is provided with a plurality of waveguides, multiplexing units that are provided at an intermediate location within the waveguides, and laser light sources, wherein: the first multiplexing unit is arranged at a position that is closest to the laser light sources; and the laser light sources that have an optical axis at a position that is separated from the transmission axis of the visible light that is introduced into the first multiplexing unit are arranged so that the optical axis is inclined with respect to the transmission axis and the outer periphery of laser light that expands at a predetermined expansion angle passes in front of the first multiplexing unit.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of U.S. application Ser. No.15/309,594, filed on Nov. 8, 2016, and wherein U.S. application Ser. No.15/309,594 is a national stage application filed under 35 U.S.C. § 371of International Application No. PCT/JP2015/056560, filed on Mar. 5,2015, which is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2014-097561, filed on May 9, 2014,the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a multiplexer which multiplexes aplurality of visible light rays having different wavelengths as well asan image projection apparatus and an image projection system using themultiplexer.

BACKGROUND ART

Optical coupling devices using a Mach-Zehnder interferometer(hereinafter referred to as MZI) have been known (see Patent Literature1). Displays can be expected to be more compact by using such opticalcoupling devices.

Patent Literature 1 discloses a technology for multiplexing ordemultiplexing two visible light rays having different wavelengthsthrough the use of a phase difference due to the difference in theoptical path length in an MZI optical waveguide into which the twovisible light rays enter. However, the technology in Patent Literature 1can multiplex only two light rays having different wavelengths, andtherefore cannot be applied to image forming apparatuses that need tomultiplex at least three visible light rays of R, G and B.

Therefore, as shown in Patent Literature 2, the present applicant hasproposed a multiplexer and an image projection apparatus that make itpossible to project an image in the image projection apparatus bymultiplexing three visible light rays of R, G and B, which are the threeprimary colors of light.

FIGS. 10A and 10B are diagrams illustrating the multiplexer that hasbeen disclosed by the present applicant in Patent Literature 2. FIG. 10Ais a plan diagram, and FIG. 10B is a side diagram showing themultiplexer, where the incident ports of the waveguides are exposed.

A multiplexer 10′ is provided with a substrate 210 formed of silicon(Si), a BOX layer 215 formed of silicon dioxide (SiO₂) on the substrate210, a cover layer 220 formed of SiO₂ on the BOX layer 215, and a firstwaveguide 101, a second waveguide 102′ and a third waveguide 103′ thatare formed in the cover layer 220 and placed within a plane parallel tothe upper surface of the BOX layer 215.

Here, the substrate 210, the BOX layer 215 and the cover layer 220 formthe main body 100 of the multiplexer 10.

A red light ray (R) having a wavelength λR of 620 to 750 nm, a greenlight ray (G) having a wavelength λG of 495 to 570 nm, and a blue lightray (B) having a wavelength λB of 450 to 495 nm, which are in a singlemode having different wavelengths, enter into the first waveguide 101,the second waveguide 102′ and the third waveguide 103′ through theincident ports 101 a′, 102 a′ and 103 a′ that are exposed from one endface of the BOX layer 215 and the cover layer 220. The RGB light raysrespectively propagating through the first waveguide 101, the secondwaveguide 102′ and the third waveguide 103′ are multiplexed and emittedfrom the other end 102 b′ of the second waveguide 102′ that is exposedfrom the other end face of the clad layer 220.

The first waveguide 101, the second waveguide 102′ and the thirdwaveguide 103′ are placed at intervals that can prevent stray light frombeing generated. A first multiplexing unit 110, a second multiplexingunit 120 and a third multiplexing unit 130 are provided along the pathof the second waveguide 102′ through which visible light propagatesstarting from the incident port 102 a′ side. The first multiplexing unit110, the second multiplexing unit 120 and the third multiplexing unit130 are formed as directional couplers in such a manner that the thirdwaveguide 103′ makes contact with the second waveguide 102′ in the firstmultiplexing unit 110 and in the third multiplexing unit 130, and thefirst waveguide 101′ makes contact with the second waveguide 102′ in thesecond multiplexing unit 120 so that the visible light rays R, G and Bcan be multiplexed.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Laid-open Patent Publication No.2010-134224

Patent Literature 2: Japanese Laid-open Patent Publication No.2013-195603

SUMMARY OF INVENTION Problems to be Solved by the Invention

In the above-described optical waveguide multiplexer, the incident ports101 a′, 102 a′ and 103 a′ are irradiated with laser beams throughoptical fibers or directly from semiconductor laser chips 16 a, 16 b and16 c that are attached to one end of the main body 100 as illustrated inthe figure.

As illustrated in FIG. 11, however, the laser beams that are emittedfrom optical fibers or the semiconductor laser chips 16 a, 16 b and 16 chave a spread angle θ1 with an optical axis X, along which the laserbeam normally proceeds from the emitting surface, at the center, andtherefore, such a problem arises that the first multiplexing unit 110 isirradiated with part of the laser beams that have leaked from thewaveguides 101, 102′ and 103, and thus, visible light rays other thanthe visible light rays that were originally targeted to be multiplexedmix into the first multiplexing unit 110 (hereinafter referred to asstray light).

In order to suppress the generation of such a mixture, waveguides 101,102′ and 103′ may be provided at sufficient intervals s (see FIG. 10) sothat the optical fibers and the semiconductor laser chips 16 a, 16 b and16 c can be sufficiently spaced from each other. However, such a problemarises that the greater the intervals s between the waveguides 101, 102′and 103′ are, the larger the multiplexer 10′ is scaled.

In addition, the waveguides 101, 102′ and 103′ are arranged next to eachother so as to be parallel to each other as illustrated in FIG. 10. Whenthe waveguides 101, 102′ and 103′ are close to each other with theintervals being a certain distance or less, however, light that hasoozes as an evanescent wave moves over to another waveguide that is inproximity, which allows the visible light rays that were originallytargeted to propagate to be mixed with another visible light ray so asto cause stray light. The intervals s between the waveguides 101, 102′and 103′ that can prevent such stray light from being generated areapproximately 30 μm or greater, and therefore, it is theoreticallypossible to make the waveguides 101, 102′ and 103′ close to each otherwith intervals s being approximately 30 μm.

Incidentally, semiconductor laser chips 16 a, 16 b and 16 c of which thesize is as minimal as approximately 500 μm in width, approximately 100μm in thickness, and approximately 500 μm in length have becomeavailable in the market in recent years. Even in the case where thesemiconductor laser chips 16 a, 16 b and 16 c are arranged adjacent toone another when being arranged at one end of the main body 100,however, the intervals s between the waveguides 101, 102′ and 103′ needto be 500 μm at minimum, and intervals are required between thesemiconductor laser chips 16 a, 16 b and 16 c in order to suppress theeffects due to heat emission. Because of these reasons, such a problemarises that there is a limit to which the width of the multiplexer 10′can be reduced.

Furthermore, it is necessary for the radius of curvature of the curvedportions R of the waveguides 101, 102′ and 103′ (see FIG. 10) to besufficiently large, or it is necessary for the length of the arc of thecurved portions R to be sufficiently long in order to widen theintervals s between the waveguides 101, 102′ and 103′ from the firstmultiplexing unit 110 where the waveguides 101, 102′ and 103′ are insuch proximity as to almost make contact with each other. Moreover, thelaser beams have a certain spread angle, and therefore, the firstmultiplexing unit 110 is irradiated with part of the spread laser beams,which causes stray light in the case where the semiconductor laser chips16 a, 16 b and 16 c are arranged side by side as described above.Because of these problems, there is also a limit to which the length ofthe multiplexer 10′ can be reduced.

The present invention is provided in view of the above-describedproblems, and an object of the invention is to provide a multiplexer inwhich the effects on the multiplexing units of the spreading of thelaser beams from the laser beam sources such as the optical fibers orsemiconductor laser chips can be suppressed, and the width and thelength of the multiplexer can be greatly reduced as long as stray lightis not generated. Another object of the invention is to provide an imageprojection apparatus using the multiplexer and an image projectionsystem.

Means for Solving the Problems

A multiplexer that can wavelength multiplex a plurality of visible lightrays having different wavelengths, comprising: a plurality of waveguidesinto which the visible light rays enter; a plurality of multiplexingunits that are provided in the middle of a waveguide and can mode couplethe visible light rays that propagate through at least two waveguides;and a plurality of laser beam sources for irradiating each waveguideswith the visible light rays, the multiplexer being characterized in that

the multiplexing unit placed the closest to the plurality of the laserbeam sources is a first multiplexing unit, and

all of the laser beam sources of which the optical axes are located at adistance away from the axis along which the visible light ray that isled into the first multiplexing unit propagates are arranged in such amanner that the optical axes are inclined relative to the axis alongwhich the visible light ray that is led into the first multiplexing unitpropagates so that the laser beams that spread at a predetermined spreadangle pass in front of the first multiplexing unit without irradiatingthe laser beams including the outer periphery of the laser beams for thefirst multiplexing unit to suppress the influence on the multiplexingunits of the spreading of the laser beams from the laser beam sources sothat stray light is not generated.

In the multiplexer according to the present invention, three visiblelight rays such as of three primary colors (red (R), green (G) and blue(B)) can be used. By doing this, it becomes possible to apply themultiplexer according to the present invention to an image projectionapparatus. That is to say, the multiplexer can be provided with: a firstwaveguide into which a first visible light ray enters; a secondwaveguide into which a second visible light ray of which the wavelengthis shorter than that of the first visible light ray enters; a thirdwaveguide into which a third visible light ray of which the wavelengthis shorter than that of the second visible light ray enters, where thedifference in the wavelength between the second visible light ray andthe third visible light ray is smaller than that between the firstvisible light ray and the second visible light ray; a first multiplexingunit and a third multiplexing unit that mode couple visible light raysbetween the second waveguide and the third waveguide, a secondmultiplexing unit that mode couples visible light rays between the firstwaveguide and the second waveguide and three laser beam sources whichirradiate the first waveguide, the second waveguide and the thirdwaveguide with the first visible light ray, the second visible light rayand the third visible light ray, respectively, where the firstmultiplexing unit, the second multiplexing unit and the thirdmultiplexing unit are arranged in this order starting from the threelaser beam sources side, and the multiplexer can have such aconfiguration where the laser beam sources for the first waveguide andthe third waveguide are arranged in such a manner that the optical axisof each laser beam source is inclined relative to the axis along which avisible light ray propagates so that the laser beams that spread at apredetermined spread angle pass in front of the first multiplexing unitwithout irradiating the laser beams including the outer periphery of thelaser beams for the first multiplexing unit to suppress the influence onthe multiplexing units of the spreading of the laser beams from thelaser beam sources so that stray light is not generated. In addition,one laser beam source of the plurality of laser beam sources may bearranged on the axis along which the visible light ray that is led intothe first multiplexing unit propagates and the other laser beam sourcesmay be arranged in such a manner that each optical axis is inclinedrelative to the axis along which the visible light ray that is led intothe first multiplexing unit propagates.

Thus, the optical axis of a predetermined laser beam source is inclinedrelative to the axis along which a visible light ray that is led intothe first multiplexing unit propagates so that stray light can besuppressed from being generated by irradiating the first multiplexingunit with part of a laser beam.

The angle of inclination can be found by the distance between theincident port of the waveguide and the incident portion of the firstmultiplexing unit, the intervals between the waveguides, and the angleat which the laser beam spreads from the laser beam source. When a laserbeam source is inclined, the laser beam crosses another waveguide with arisk of the stray light affecting the waveguide. Even in such a case,the effects of stray light on the waveguide can be suppressed to theminimum by adjusting the angle of inclination θ in a range of 0°<θ≤90°.In addition, the size of the multiplexer can be made minimum byadjusting the angle of inclination θ to a right angle.

A bending unit that can change the direction of the visible light raythat propagates along a waveguide in such a manner that the optical pathof the visible light is bent may be provided between the firstmultiplexing unit and another laser beam source. The bending unit may beable to bend the direction in which a visible light ray propagatesthrough a waveguide at an angle, which is formed when two linesintersect. Examples can be cited such as a diffraction grating formed ina part of a waveguide, a mirror (waveguide type reflector) formed bycreating a trench in the direction towards the core of the waveguide,and a mirror provided by vapor depositing aluminum on the outside of thecore of a waveguide.

The use of such a bending unit makes it possible to provide a laser beamsource at one end and on the sides of the main body of the multiplexer,and thus makes it possible to greatly reduce the width and the length ofthe multiplexer. In addition, the use of such a bending unit increasesthe degree of freedom in the arrangement of the laser beam sources suchas semiconductor laser chips, and therefore also increases the degree offreedom in designing an image projection apparatus or the like thatutilizes the multiplexer according to the present invention.

A light converging means may be provided at an incident port for a laserbeam from a laser beam source in a waveguide. For example, an endportion of the waveguide may be tapered, or a lens may be providedbetween the laser beam source and the waveguide.

Though the angle at which the bending unit bends the optical path is notparticularly limited, it is preferable for the angle to be within arange from 80° to 100° in the case where a waveguide type reflector isused, for example. It is more preferable for the angle to be a rightangle.

An image projection apparatus using the multiplexer according to thepresent invention uses a multiplexer having the above-describedstructure that is provided with: a horizontal scanning unit and avertical scanning unit that can two-dimensionally scan an object withthe wavelength multiplexed light emitted from the multiplexer so as toform an image; and an image forming unit that projects the resultingimage from the scanning with the wavelength multiplexed light onto asurface on which an image is to be projected. In such a case, themultiplexer may be provided with the horizontal scanning unit and thevertical scanning unit. By doing this, the image projection apparatuscan be made compact.

In addition, an image projection system having an image projectionapparatus as described above can be formed of: a transmission andreceiving apparatus for transmitting and receiving image data; aperipheral apparatus that includes an image taking apparatus such as acamera or a terminal apparatus such as a mobile phone or a PC; and acontrol apparatus for controlling the transmission and receivingapparatus, the peripheral apparatus and the image projection apparatus.

The image projection apparatus according to the present invention, wherea multiplexer having the above-described structure is used, as well asan image projection system provided with such an image projectionapparatus make it possible to make the apparatus and the system compactdue to the multiplexer that has been made compact, and in addition canincrease the freedom in designing the apparatus and the system due to ahigh level of freedom in the arrangement of the light sources such assemiconductor laser chips provided in the multiplexer.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the basic concept of the presentinvention and the arrangement of the laser beam sources for threevisible light rays;

FIG. 2A is a diagram illustrating the relationship between a laser lightsource and a waveguide in the case of the arrangement in FIG. 1;

FIG. 2B is a diagram illustrating another case where a bending unit forbending the optical path to a right angle is provided in the middle of awaveguide;

FIG. 3 is a schematic plan diagram illustrating the multiplexer having abending unit for bending the optical path to a right angle according toone embodiment;

FIGS. 4A and 4B are diagrams illustrating an enlarged portion of thestructure of a bending unit in a waveguide;

FIGS. 5A and 5B are diagrams illustrating an enlarged portion at an endof a waveguide provided with a light converging means;

FIG. 6 is a schematic diagram illustrating the configuration of ascanning type display according to one embodiment where the multiplexer10 according to the present invention is applied to the scanning typedisplay;

FIG. 7 is a schematic diagram illustrating the multiplexer 10 where ahorizontal scanner 22 and a vertical scanner 25 are arranged on theother end 102 b side of the second waveguide 102;

FIG. 8 is a block diagram illustrating the configuration of one exampleof an image system having a scanning type display;

FIGS. 9A and 9B are diagrams illustrating examples of the arrangement ofsemiconductor laser chips in the case of the multiplexer formultiplexing four or more visible light rays according to anotherembodiment of the present invention;

FIGS. 10A and 10B are diagrams illustrating the multiplexer that hasbeen disclosed in Patent Literature 2 by the present applicant, whereFIG. 10A is a plan diagram, and FIG. 10B is a front diagram illustratingthe multiplexer as viewed from one end side where the incident ports ofthe waveguides are exposed; and

FIG. 11 is a diagram illustrating how the first multiplexing unit isirradiated with laser beams emitted from laser beam sources due to thespreading of the laser beams.

DESCRIPTION OF EMBODIMENTS

In the following, the preferred embodiments of the present invention aredescribed in detail in reference to the drawings.

FIG. 1 is a diagram illustrating the basic concept of the presentinvention and illustrates the arrangement of laser beam sources in acase where three visible light rays are used. FIG. 2A is a diagramillustrating the relationship between a laser beam source and awaveguide in the case of the arrangement in FIG. 1, and FIG. 2B is adiagram illustrating another example in a case where a bent portion thatbends at right angles is provided in the middle of a waveguide. FIG. 3is a schematic plan diagram illustrating the multiplexer having bentportions that bend at right angles according to one embodiment. FIGS. 4Aand 4B are diagrams illustrating an enlarged portion of the structure ofa bent portion. FIGS. 5A and 5B are diagrams illustrating an enlargedportion at an end of a waveguide provided with a light converging means.

[Visible Light Rays that can be Used]

The below-described three visible light rays that are multiplexed by themultiplexer according to the present invention are monochromatic raysunder such conditions that the wavelength of the first visible light rayis the longest, followed by the wavelength of the second visible lightray with the wavelength of the third visible light ray being theshortest, and the difference in the wavelength between the secondvisible light ray and the third visible light ray is smaller than thatbetween the first visible light ray and the second visible light ray.

A red light ray (R) having a wavelength λR=620 to 750 nm, a green lightray (G) having a wavelength λG=495 to 570 nm, and a blue light ray (B)having a wavelength λB=450 to 495 nm can be cited as examples of thevisible light rays that satisfy the above-described conditions. Therelationship of λB<λG<λR is formed between the three wavelengths of R, Gand B, and from among the wavelength ranges that satisfy therelationship, a red light ray having a wavelength λR=640 nm, a greenlight ray having a wavelength λG=520 nm, and a blue light ray having awavelength λB=455 nm can be selected as an example that satisfies therelationship of λR−λG>λG−λB.

[Arrangement of Laser Beam Sources]

In this embodiment, a semiconductor laser chip 16 a for red light and asemiconductor laser chip 16 c for blue light from among threesemiconductor laser chips 16 a, 16 b and 16 c are arranged in such amanner that the optical axes Xr and Xb of the semiconductor laser chips16 a and 16 c cross the Y axis along which light propagates at an angleθ as illustrated in FIG. 1.

In this embodiment, the two semiconductor laser chips 16 a and 16 c arearranged in such a manner that the optical axes of these chips inclineat an angle θ relative to the Y axis along which light propagatesbecause of the following reasons. That is to say, the semiconductorlaser chips 16 a and 16 c have optical axes Xb and Xr at locations thatare at a distance away from the Y axis of the first multiplexing unit110 along which the visible light rays propagate, where the firstmultiplexing unit 110 is the closest to the semiconductor laser chipsfrom among the multiplexing units. In the case where the twosemiconductor laser chips 16 a and 16 c are arranged in such a mannerthat the optical axes Xb and Xr are parallel to the Y axis along whichthe visible light rays propagate (see FIG. 11), the multiplexing unit110 is irradiated with the laser beams that spread at an angle θ1, andthus, stray light is generated and affects the multiplexing.

Meanwhile, the semiconductor laser chip 16 b for green light that isarranged in the middle has an optical axis Xg at approximately the samelocation at that of the Y axis along which visible light rays propagate,and therefore, the irradiation of the multiplexing unit 110 with thelaser beam that spreads at an angle θ1 hardly allows stray light toaffect the first multiplexing unit 110.

As illustrated in this embodiment, in the case where laser beams are ledfrom the three semiconductor laser chips 16 a, 16 b and 16 c to thethree waveguides 101, 102 and 103 in order to multiplex visible lightrays, the semiconductor laser chips 16 a and 16 c on the two sides aregenerally inclined and the semiconductor laser chip 16 b in the middledoes not need to be inclined.

The angle θ is an angle that prevents the first multiplexing unit 110,which is the multiplexing unit closest to the semiconductor laser chips16 a, 16 b and 16 c, from being irradiated with the laser beams from thesemiconductor laser chips 16 a and 16 c that spread with the opticalaxes Xr and Xb at the center.

The angle θ can be found in the following formula when the angle atwhich the laser beams spread is θ01, the distance between the incidentports 101 a and 102 a (or between 102 a and 103 a) is d1, and thedistance between the incident port 102 a and the incident portion of thefirst multiplexing unit 110 is I1.θ>½θ1+arctan(d1/I1)  [Formula 1]

In the case of the angle at which the laser beams spread being 01=7°,the distance d1=500 μm, and the distance I1=900 μm, θ=35.5° is found,and therefore, the angle θ can be made greater than 35.5° so that thefirst multiplexing unit 110 can be prevented from being irradiated withspread laser beams from the semiconductor laser chips 16 a and 16 c.

Though the angle θ may be an acute angle as illustrated in FIG. 2A, itis preferable for it to be a right angle as illustrated in FIG. 2B. Bydoing this, the irradiated length e of the waveguide 102 portion that isirradiated with the laser beam from the semiconductor laser chip 16 acan be made shortest, which can minimize the effects of stray light onthe visible light rays that propagate through the waveguide 102.

In the case where the angle θ is made a right angle, bending units 104and 105 that reflect visible light rays are provided in the middle ofthe waveguides 101 and 103 in order to maintain the propagationefficiency of the visible light rays that propagate through thewaveguides 101 and 103. The bending units 104 and 105 are bent at rightangles, which are formed when two lines intersect orthogonally. In orderto allow the visible light rays to propagate efficiently through theportions of the waveguides 101 and 103 that are bent beyond the criticalangle, the below-described mirrors 104 a and 105 a and diffractiongratings 104 b and 105 b are provided in the bent portions.

[Entire Configuration of Multiplexer]

FIG. 3 illustrates the multiplexer having bending units that are bent atright angles according to one embodiment of the present invention.

The basic structure of the multiplexer 10 is the same as that of themultiplexer disclosed in Japanese Unexamined Patent Publication2013-195603 by the present applicant (shown in FIG. 10). The samesymbols are attached to the same components as in the multiplexer 10′ inFIG. 10, and the detailed descriptions thereof are not repeated.

The multiplexer 10 is different from the multiplexer 10′ in FIG. 10 inthe point that end portions of the first waveguide 101 and the thirdwaveguide 103 are bent or curved so that the directions in which visiblelight rays B and R enter into the first waveguide 101 and the thirdwaveguide 103 cross the direction in which the wavelength multiplexedvisible light rays are emitted from the second waveguide 102.

Bending units 104 and 105 are provided in end portions of the firstwaveguide 101 and the third waveguide 103 so that the optical paths ofthe first visible light ray and the third visible light ray that haveentered through the incident ports 101 a and 103 a can be changed withinthe first waveguide 101 and the third waveguide 103. Thus, the firstwaveguide 101 and the third waveguide 103 are bent or curved in theseportions where the bending units 104 and 105 are provided.

FIGS. 4A and 4B illustrate an example of the bending unit 104 or 105.

In the example in FIG. 4A, a mirror 104 a or 105 a that totally reflectsvisible light is arranged in the bending unit 104 or 105, and the firstwaveguide 101 or the third waveguide 103 is bent at this portion.

In this embodiment, the mirror 104 a or 105 a is of a waveguide typewhere the cover layer 220 is etched from the upper surface so as tocreate a trench that reaches a portion deeper than the core of the firstwaveguide 101 or the third waveguide 103, and light is totally reflectedfrom the interface between the air layer of the trench and the glasslayer that forms the core.

In such a waveguide type mirror, the ratio of light that enters lowers,and at the same time, the reflectance lowers when the angle α at whichthe waveguide is bent shifts from the right angle (90°) to an angle thatis either greater or smaller. Therefore, the optimal angle α at whichthe waveguide is bent in such a waveguide type mirror is 90°. However,the allowable angle α at which the waveguide is bent in the case where50% is the standard ratio of light that enters is within a range from77° to 100°, and is preferably within a range from 80° to 95°.

In the example illustrated in FIG. 4B, a diffraction grating 104 b or105 b is formed in the bending unit 104 or 105. Thus, the waveguide 101or 103 is bent at an angle α in the portion where the diffractiongrating 104 b or 105 b is formed.

In addition, the first waveguide 101 or the third waveguide 103 may becurved with a curvature radius R. The curved portion 104 c or 105 c maybe provided with a reflection means such as a mirror or a diffractiongrating if necessary.

As other means for changing the optical path in a portion that is bentat a certain angle or curved, those that are publicly-known in JapaneseUnexamined Patent Publication 2004-191564 and Japanese Unexamined PatentPublication H10 (1998)-246827 can be used.

[Light Inputting Portion]

In this embodiment, the substrate 210 is formed a little greater thanthe cover layer 220 and the BOX layer 215 in the length and the width,and semiconductor laser chips 16 a, 16 b and 16 c, which are lightsources of visible light rays that enter into the first waveguide 101,the second waveguide 102 and the third waveguide 103, are arranged in aportion (margin) that protrudes from the cover layer 220 and the BOXlayer 215.

The semiconductor laser chips 16 a, 16 b and 16 c can be positionedrelative to the incident ports 101 a, 102 a and 103 a of the firstwaveguide 101, the second waveguide 102 and the third waveguide 103 byadjusting the thickness of the substrate 210.

As for the size of the semiconductor laser chips 16 a, 16 b and 16 c,the width is approximately 500 μm, the thickness is approximately 100μm, and the length is approximately 500 μm, and therefore, thesemiconductor laser chips 16 a, 16 b and 16 c can be provided so as tobe integrated with the optical multiplexer 10.

In addition, it is preferable for the incident ports 101 a, 102 a and103 a of the first waveguide 101, the second waveguide 102 and the thirdwaveguide 103 to be provided with a laser beam converging means so thatthe laser beams from the semiconductor laser chips 16 a, 16 b and 16 ccan be led to the waveguides 101, 102 and 103 with high efficiency.

FIGS. 5A and 5B illustrate an example of a laser beam converging means.Though FIGS. 5A and 5B illustrate only a case of the first waveguide 101as an example, the same laser beam converging means can be applied tocases of the second waveguide 102 and the third waveguide 103.

In the example in FIG. 5A, the first waveguide 101 is formed with oneend being tapered. The standard shape of the taper ((D−d)/L) may beapproximately 1/100.

In the example in FIG. 5B, a microscopic lens 17 is arranged between thesemiconductor laser chip 16 a and the incident port 101 a.

By providing such a laser beam converging means, a visible light rayfrom a microminiature laser beam source such as the semiconductor laserchips 16 a, 16 b and 16 c can be made to enter into the waveguide 101,102 or 103 with high efficiency.

[Working Effects]

In the multiplexer 10 having the above-described structure, end portionsof the first waveguide 101 and the third waveguide 103 on either side ofthe second waveguide 102 that runs straight from among the threewaveguides 101, 102 and 103 are bent at approximately right angles inthe bending units 104 and 105, and thus, it is possible to locate theincident port 101 a of the first waveguide 101 and the incident port 103a of the third waveguide 103 on the sides of the main body 100 of themultiplexer 10 that face each other. In addition, it is possible toarrange the semiconductor laser chip 16 b that emits a green light rayinto the second waveguide 102, from among the semiconductor laser chips16 a, 16 b and 16 c that are laser beam sources, at one end of the mainbody 100 of the multiplexer 10, and it is also possible to arrange thesemiconductor laser chips 16 a and 16 c that emit a red light ray and ablue light ray on either side of the main body 100 of the multiplexer10.

Therefore, the total length of the main body 100 can be made shorter bythe length of the bent portions of the first waveguide 101 and the thirdwaveguide 103. In addition, the entire width of the main body 100 can bemade narrower by arranging the semiconductor laser chips 16 a and 16 con the sides of the main body 100, which can narrow the distance sbetween the first waveguide 101 and the second waveguide 102 as well asbetween the third waveguide 103 and the second waveguide 102. Thus, thelight source integrated type multiplexer 10 having the semiconductorlaser chips 16 a, 16 b and 16 c can be made compact. Furthermore, thelocations at which the semiconductor laser chips 16 a and 16 c arearranged can be changed by appropriately changing the angle α at whichthe waveguides are bent so that the freedom in designing the multiplexer10 can be increased.

[Configuration of Scanning Type Display]

FIG. 6 is a schematic diagram illustrating the configuration of ascanning type display in an embodiment where a multiplexer 10 having theabove-described structure is applied to the scanning type display.

As illustrated in FIG. 6, a scanning type display 1 has a control unit 1a and a display unit 1 b that are integrally formed.

The display unit 1 b can be worn on the head of the user together withthe control unit 1 a by using a glass frame type fitting apparatus asdisclosed in U.S. Unexamined Patent Publication 2010/0073262.

The control unit 1 a has a controller 12, an operation unit 13, anexternal interface (I/F) 14, an R laser driver 15 a, a G laser driver 15b, a B laser driver 15 c and the multiplexer 10 that is integrallyequipped with the semiconductor laser chips 16 a, 16 b and 16 c. Thecontroller 12 is formed of a microcomputer that includes a CPU, a ROM, aRAM and the like. The controller 12 generates an R signal, a G signal, aB signal, a horizontal signal and a vertical signal that becomecomponents for synthesizing an image on the basis of the image data thatis supplied from the external apparatus such as a PC through theexternal I/F 14. The controller 12 transmits the R signal to the R laserdriver 15 a, transmits the G signal to the G laser driver 15 b, andtransmits the B signal to the B laser driver 15 c, respectively.

The controller 12 transmits the horizontal signal to the horizontalscanning driver 23 and transmits the vertical signal to the verticalscanning driver 26, respectively. The horizontal signal and the verticalsignal include a sync signal for determining the timing in the operationof a horizontal scanner 22 and a vertical scanner 25, and a drivesetting signal for setting the voltage and the frequency of the drivesignal that is transmitted to the horizontal scanner 22 and the verticalscanner 25 from the horizontal scanning driver 23 and the verticalscanning driver 26.

The operation unit 13 is formed of various types of buttons that acceptthe operation by the user and an interface circuit that transmits to thecontroller 12 an operation signal that is generated when a button ispressed. The various types of buttons that accept the operation by theuser are provided on the surface of the housing of the control unit 1 a,for example. The external I/F 14 is an interface for electricallyconnecting the control unit 1 a to an external apparatus such as a PC.

The R laser driver 15 a drives the semiconductor laser chip 16 a so thata red laser beam is generated of which the intensity of the light is inresponse to the R signal from the controller 12. The G laser driver 15 bdrives the semiconductor laser chip 16 b so that a green laser beam isgenerated of which the intensity of the light is in response to the Gsignal from the controller 12. The B laser driver 15 c drives thesemiconductor laser chip 16 c so that a blue laser beam is generated ofwhich the intensity of the light is in response to the B signal from thecontroller 12. It is possible to synthesize a laser beam having adesired color by adjusting the ratio of intensities of the laser beamshaving the respective colors. The laser beams having the respectivecolors generated by the semiconductor laser chips 16 a, 16 b and 16 center into the waveguides 101, 102 and 103 of the multiplexer 10,respectively, and are multiplexed into a wavelength multiplexed lightbeam, which is emitted from the multiplexer 10 in this state. Theemitted laser beam is conveyed to the display unit 1 b through anoptical fiber that is included in the signal line.

The display unit 1 b has a collimating optical system 21, the horizontalscanner 22, the horizontal scanning driver 23, a relay optical system 24equipped with lenses 24 a and 24 b, the vertical scanner 25, thevertical scanning driver 26, and an ocular optical system 27 equippedwith lenses 27 a and 27 b.

The collimating optical system 21 converts the laser beam emitted fromthe optical fiber to a parallel beam. The laser beam that has beenconverted to a parallel beam enters into the horizontal scanner 22.

The horizontal scanner 22 operates the laser beam from the collimatingoptical system 21 in the horizontal direction. Typically, the horizontalscanner 22 has a reflection plane that fluctuates. When the reflectionplane fluctuates, the laser beam that is incident on the reflectionplane is scanned in the horizontal direction. It is possible to form thehorizontal scanner 22 of a resonant type MEMS (microelectromechanicalsystem) mirror that fluctuates using a piezoelectric element. Thehorizontal scanning driver 23 controls the fluctuations of thehorizontal scanner 22 in accordance with the horizontal sync signal fromthe controller 12. The laser beam scanned horizontally is incident onthe relay optical system 24.

The vertical scanner 25 scans the laser beam from the relay opticalsystem 24 in the vertical direction. Typically, the vertical scanner 25has a reflection plane that fluctuates. When the reflection planefluctuates, the laser beam that is incident on the reflection plane isscanned in the vertical direction. It is possible to form the verticalscanner 25 of an MEMS mirror that fluctuates, for example. The verticalscanning driver 26 controls the fluctuations of the vertical scanner 25in accordance with the vertical sync signal from the controller 12.Here, an object has been scanned with the laser beam in the horizontaldirection by the horizontal scanner 22, and therefore, the object istwo-dimensionally scanned when the object is scanned vertically by thevertical scanner 25 so as to provide an image. The light from the imageresulting from the two-dimensional scanning is incident on the ocularoptical system 27.

It is possible to provide the horizontal scanner 22 and the verticalscanner 25 so as to be integrated with the multiplexer 10 according tothe present invention.

FIG. 7 is a schematic diagram illustrating the multiplexer 10 where thehorizontal scanner 22 and the vertical scanner 25 are arranged on theother end 102 b side of the second waveguide 102.

Thus, the horizontal scanner 22 and the vertical scanner 25 are providedso as to be integrated with the multiplexer 10 so that the relay opticalsystem 24 and the collimating optical system 21 can be made unnecessary.In addition, the horizontal scanning driver 23 and the vertical scanningdriver 26 are incorporated into the control apparatus 12 so that theconfiguration can be simplified by integrating the control unit 1 a andthe display unit 1 b, and the scanning type display 1 can be madecompact.

FIG. 8 is a block diagram illustrating an example of the configurationof an image system that is provided with a scanning type display havingthe above-described configuration.

A controller 19 receives signals of images taken by a camera 17 andimage data stored in a memory of a personal computer or the like andallows the scanning type display 1 to display the corresponding image.In addition, a transmission/receiving unit 18 is connected to thecontroller 19, which makes possible the connection to an external serveror computer, the Internet, a portable phone and the like. Here, it ispossible to use the controller 12 of the scanning type display as thecontroller 19. Thus, the use of the multiplexer 10 according to thepresent invention makes it possible to make such an image system ascompact as a 1 cm square or less.

EXAMPLE

Next, a typical example of the multiplexer 10 according to the presentinvention is described.

In this example, a BOX layer 215 having a thickness of 15 μm is formedthrough deposition on top of a rectangular substrate 210 formed of SiO₂and having a thickness of 35 μm, a length of 6 mm and a width of 1 mm,and three waveguides 101, 102 and 103 are formed on the upper surface ofthe BOX layer 215. The waveguides 101, 102 and 103 are made of SiO₂glass doped with GeO₂ so as to have a difference of 0.5% in therefractive index with the surrounding clad. The waveguides 101, 102 and103 have a cross-section of a 2 μm square. In addition, the waveguides101, 102 and 103 are covered with a cover layer 220 made of SiO₂ glasshaving a thickness of 20 μm.

The BOX layer 215 and the cover layer 220 are slightly smaller than thesubstrate 210 so as to be provided with margins on one end side and onthe left and right sides, where semiconductor laser chips 16 a, 16 b and16 c having such a size that the width is 500 μm, the thickness is 100μm, and the length is 500 μm can be mounted on the substrate 210. Here,as the substrate 210, a substrate doped with a high concentration p typedopant having high heat radiating properties (with a resistance value of1000 Ωcm) is used so that the heat from the semiconductor laser chips 16a, 16 b and 16 c can be easily released.

Bending units 104 and 105 for changing the direction of the optical pathby a right angle (90°) are provided in places that are 300 μm away fromthe incident ports 101 a and 103 a of the waveguides 101 and 103. Thebending units 104 and 105 have a rectangular trench created from thesurface of the cover layer 220 up to a depth of 25 μm so as to have sucha size that the width is 10 μm and the length is 5 μm, where the innerwall surfaces of these trenches orthogonally cross the inner wallsurface of the core of the waveguides 101 and 103.

The critical angle for the total reflection of light from a wall surfaceof the above-described trenches is found to be 43.6° when the refractiveindex of SiO₂ based glass is 1.45, and thus, the optical path can bechanged by an angle of 87.2°, which is almost a right angle.

The semiconductor laser chips 16 a, 16 b and 16 c are attached to theabove-described margins of the substrate 210. As for the size of thesubstrate 210, the length is 6 mm and the width is 1 mm, while the sizeof the multiplexer 10 including the semiconductor laser chips 16 a, 16 band 16 c is such that the length is 7 mm, the width is 2 mm, and thethickness is 500 μm.

In the multiplexer 10 having this size, the first multiplexing unit 110is slightly affected by stray light due to a visible light ray thatspreads at an angle θ1, even in the case where the optical axis Xg ofthe semiconductor laser chip 16 b is almost in the same location as orslightly shifted from the Y axis along which the visible light raypropagates (the amount of shift is approximately +/−30 μm or less), andtherefore, the semiconductor laser chip 16 b does not need to beinclined.

RGB visible light rays from the semiconductor laser chips 16 a, 16 b and16 c is incident on the waveguides 101, 102 and 103 in the multiplexer10 having the above-described configuration. As a result, it was foundthat the distribution of the optical power in the lateral directionshifted from the stable propagation mode immediately after the visiblelight rays had been reflected from the wall surface of the trench insuch a manner that the direction of the optical path was changed by aright angle. As a result of a simulation, however, it was found that thedistribution of the optical power settled in a stable mode when thevisible light rays propagated through the waveguides 101 and 103 at adistance that was ten or more times greater than the wavelength.

In addition, it was found that the ratio of the visible light rays thatmove over from the waveguides 101 and 103 to the waveguide 102 could bemade so small as to be negligible when the distance a of the linearportion of the optical path after the direction had been changed in FIG.4A was ten or more times greater than the wavelength. As a result, it isnot necessary to make length of the multiplexing units 110, 120 or 130longer, which does not make the total length of the multiplexer 10 longwhen the distance a is ten or more times greater than the wavelength.

Though the preferred embodiments of the present invention are describedin the above, the present invention is not limited to these embodiments.

For example, the semiconductor laser chip 16 may be arranged so as to beinclined in such a manner that the optical axis Xg crosses the Y axisalong which the visible light rays propagate.

Though RGB light rays are cited as examples of three visible light raysin the description, the application of the multiplexer according to thepresent invention is possible for three visible light rays other than R,G and B. In addition, the application to a multiplexer for multiplexingfour or more visible light rays is possible. In this case, for example,semiconductor laser chips 16 a through 16 d may be arranged asillustrated in FIGS. 9A and 9B.

Furthermore, the arrangement of the waveguides 101, 102 and 103 as wellas the semiconductor laser chips 16 a, 16 b and 16 c are not limited toa two-dimensional arrangement as in the above. A three-dimensionalarrangement is possible in such a manner where, for example, thewaveguides 101 and 103 as well as the semiconductor laser chips 16 a and16 c are arranged along the circumference with the waveguide 102 at thecenter.

Though the waveguides 101, 102 and 103 are formed integrally by buryingthe core layer inside the cover layer 220 in the above description, thewaveguides 101, 102 and 103 that are made of a core layer and a cladlayer may be formed separately so as to be arranged on a support such asa substrate.

Though waveguide type mirrors are cited as examples in the aboveembodiments, other types of mirrors may be used, and an example of suchmirrors is mirror surfaces formed on the outside of the cores of thefirst waveguide 101 and the third waveguide 103 through vapor depositionof aluminum.

INDUSTRIAL APPLICABILITY

The multiplexer according to the present invention can be applied widelyto apparatuses for projecting images where a plurality of visible lightrays that are monochromatic rays are multiplexed, and thus, applicationis possible to a retina scanning type display where a retina of the useris scanned with multiplexed light rays for image projection and to alaser display that uses laser beam scanning for image projection.

REFERENCE SIGNS LIST

-   -   1 a control unit    -   1 b display unit    -   10 multiplexer    -   101 first waveguide    -   102 second waveguide    -   103 third waveguide    -   104, 105 bending unit    -   104 a, 105 a mirror    -   104 b, 105 b diffraction grating    -   104 c, 105 c curved portion    -   110 first multiplexing unit    -   120 second multiplexing unit    -   130 third multiplexing unit    -   16 a, 16 b, 16 c semiconductor laser chip

The invention claimed is:
 1. A multiplexer that can wavelength multiplexa plurality of visible light rays having different wavelengths,comprising: a plurality of waveguides into which the visible light raysenter; a plurality of multiplexing units that are provided in the middleof a waveguide and can mode couple the visible light rays that propagatethrough at least two waveguides; and a plurality of laser beam sourcesfor irradiating each waveguides with the visible light rays, wherein themultiplexing unit placed the closest to the plurality of laser beamsources is a first multiplexing unit, and all of the laser beam sourcesof which the optical axes are located at a distance away from the axisalong which the visible light ray that is led into the firstmultiplexing unit propagates are arranged in such a manner that theoptical axes are inclined relative to the axis along which the visiblelight ray that is led into the first multiplexing unit propagates sothat the outer peripheries of the laser beams that spread at apredetermined spread angle pass in front of the first multiplexing unitwithout irradiating the first multiplexing unit with the laser beams tosuppress the influence on the first multiplexing unit of the spreadingof the laser beams from the laser beam sources so that stray light isnot generated.